U.S. patent application number 11/354635 was filed with the patent office on 2006-08-10 for electrical isolation connector subassembly for use in directional drilling.
Invention is credited to Rishi Gurjar, Michael T. Sutherland.
Application Number | 20060175826 11/354635 |
Document ID | / |
Family ID | 32908093 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175826 |
Kind Code |
A1 |
Sutherland; Michael T. ; et
al. |
August 10, 2006 |
Electrical isolation connector subassembly for use in directional
drilling
Abstract
An electrical isolation connector subassembly for
interconnecting adjacent tubular drill rods of a drilling system
used in drilling bore holes in earth formations, the connector
comprising an electrically insulative sleeve being sandwiched
between two electrically isolated subassembly components, the
sleeve providing an exterior gap between the edges of the spaced
apart electrically isolated components, the exterior gap having a
width of less than 50 cm.
Inventors: |
Sutherland; Michael T.;
(Calgary, CA) ; Gurjar; Rishi; (Edmonton,
CA) |
Correspondence
Address: |
BARNES & THORNBURG, LLP
P.O. BOX 2786
CHICAGO
IL
60690-2786
US
|
Family ID: |
32908093 |
Appl. No.: |
11/354635 |
Filed: |
February 15, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10377214 |
Feb 28, 2003 |
7032930 |
|
|
11354635 |
Feb 15, 2006 |
|
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Current U.S.
Class: |
285/47 |
Current CPC
Class: |
E21B 17/003
20130101 |
Class at
Publication: |
285/047 |
International
Class: |
F16L 59/16 20060101
F16L059/16 |
Claims
1. An electrical isolation connector subassembly for
interconnecting adjacent tubular drill rods of a drilling system
used in drilling bore holes in earth formations, said connector
comprising an electrically insulative sleeve being sandwiched
between two electrically isolated subassembly components, the
sleeve providing an exterior gap between the edges of the spaced
apart electrically isolated components, the exterior gap having a
width of less than 50 cm.
2. The electrical isolation connector subassembly of claim 1,
wherein the electrically isolated first and second components of
the subassembly are isolated by insulator sleeves.
3. The electrical isolation connector subassembly of claim 1,
wherein the insulator sleeves are removable and reusable.
4. The electrical isolation connector subassembly of claim 1,
wherein the components are interconnected by threaded engagement,
at least one stop defining the exterior gap distance between
opposing edges of the first and second components so as to sandwich
the insulative sleeve and slightly compress it.
5. An electrical isolation connector subassembly for
interconnecting adjacent tubular drill rods of a drilling system
used in drilling bore holes in earth formations, said connector
comprising: a first electrically isolated component; a second
electrically isolated component; a plurality of insulator sleeves;
the first electrically isolated component being adapted on one end
to connect to a first tubular drill rod; the second electrically
isolated component being adapted on one end to connect to a second
tubular drill rod; said plurality of insulator sleeves electrically
separating said first and second electrically isolated components;
wherein at least one of said insulator sleeves is sandwiched
between the first and second electrically isolated components,
providing an exterior gap between the edges of the spaced apart
first and second electrically isolated components, the exterior gap
having a width of less than 50 cm.
6. The electrical isolation connector subassembly of claim 5,
wherein the first electrically isolated component comprises a
mandrel and a first coupler.
7. The electrical isolation connector subassembly of claim 5,
wherein the second electrically isolated component comprises a gap
housing and a second coupler.
8. The electrical isolation connector subassembly of claim 6,
wherein the interface between said mandrel and said gap housing is
adapted to prevent longitudinal axial rotation of said gap housing
with reference to said mandrel.
9. The electrical isolation connector subassembly of claim 5,
wherein said plurality of insulator sleeves include a first
insulator sleeve, a second insulator sleeve and a third insulator
sleeve.
10. The electrical isolation connector subassembly of claim 6,
wherein a retaining nut is used to urge said gap housing towards
said mandrel, thereby imparting compressive pressure upon said
insulator sleeves to prevent the ingress of drilling mud into said
subassembly.
11. The electrical isolation connector subassembly of claim 10,
wherein said retaining nut is electrically isolated from said gap
housing using an insulator spacer.
12. The electrical isolation connector subassembly of claim 10,
wherein said retaining nut and a terminal end of said mandrel is
electrically isolated from said second coupler using an aft
insulator, said aft insulator being adapted to receive seals to
prevent thereby ingress of drilling mud into said subassembly.
13. An electrical isolation connector subassembly for
interconnecting adjacent tubular drill rods of a drilling system
used in drilling bore holes in earth formations, said connector
comprising: a mandrel, wherein said mandrel is adapted at one end
to connect to a first tubular drill rod; a housing, wherein said
housing is adapted at one end to connect to a second tubular drill
rod; a conductive ring located on an external surface of said
connector; a plurality of insulator sleeves; said mandrel and said
housing being electrically continuous; said conductive ring being
electrically isolated from said mandrel and said housing by said
insulator sleeves; an electrode assembly that engages said
conductive ring wherein said electrode assembly is electrically
isolated from said mandrel and said housing, said electrode
assembly being positioned within openings in said mandrel wherein
said openings extends perpendicular to the longitudinal axis of the
electrical isolation connector subassembly; wherein said insulator
sleeves are sandwiched between the conductive ring and adjacent
opposing faces of the subassembly, providing an exterior gap having
a width of less than 50 cm.
14. The electrical isolation connector subassembly of claim 13,
wherein said insulative sleeves include dual ring conductor
insulators and a central insulator, said ring conductor insulators
being positioned directly adjacent to each side of said conductive
ring, said central insulator having openings that align with said
openings in said mandrel and being positioned between said mandrel
and said conductive ring.
15. The electrical isolation connector subassembly of claim 13,
wherein said opening in said mandrel is electrically insulated from
said electrode assembly by transverse insulators.
16. The electrical isolation connector subassembly of claim 13,
wherein at the external surface of the connector, adjacent to each
side of said external portion of said ring conductor insulators,
are wear shoulders.
17. The electrical isolation connector subassembly of claim 13,
wherein said conductive ring is adapted to receive seals to thereby
prevent ingress of drilling mud into subassembly.
18. The electrical isolation connector subassembly of claim 13,
wherein said mandrel is adapted to receive seals to thereby prevent
ingress of drilling mud into subassembly.
19. The electrical isolation connector subassembly of claim 13,
wherein said electrode assembly is comprised of a conductor base, a
spring and a conductor cap, said spring being positioned against
conductor base and biased to impart pressure against conductor cap
thereby causing contact between said conductor cap and said ring
conductor.
20. The electrical isolation connector subassembly of claim 13,
wherein said housing and said mandrel are adapted to threadably
engage each other to thereby tighten the assembly and impart
compressive pressure upon said insulators and said conductive ring
to thereby prevent ingress of drilling mud into subassembly.
21. The electrical isolation connector of claim 1, wherein the
exterior gap has a width ranging from about 1/2 cm to less than 50
cm, preferably 1 cm to about 40 cm, more preferably 2 cm to about
30 cm, even more preferably about 3 cm to about 20 cm and most
preferably from about 5 cm to 10 cm.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an electrical isolation connector
subassembly for use in data telemetry in directional drilling
applications.
BACKGROUND OF THE INVENTION
[0002] The transmission of electromagnetic signals from a bore-hole
to the earth surface is an effective method of communicating
information during various types of drilling operations, such as
measuring while drilling (MWD) and/or logging well drilling (LWD).
The ability to communicate allows for the monitoring of drilling
operations, as well as the inspection and evaluation of surrounding
geology. During directional drilling operations, such as boring
holes under river beds, subways, unusual earth formations and
tapping oil reservoirs, it is particularly important at all times
to know precisely the location of the drill bit. A significant
effort has been made to develop electrical instruments which are
capable of transmitting signals at the drill face or inspection
face back to the earth's surface.
[0003] A number of systems have been developed which incorporate
electromagnetic technology for communicating to the earth surface.
For example, in U.S. Pat. No. 5,394,141, described is a system
where the lower portion of the drill string is used as an antenna
for purposes of transmitting electromagnetic waves carrying
information.
[0004] Various types of devices which are mounted on the outside of
the drill string for monitoring surrounding conditions and/or used
in communication are described, for example, in U.S. Pat. No.
4,684,946 to Geoservices and U.S. Pat. No. 5,467,832 to
Schlumberger Technology Corporation. The problem with mounting
communication devices and sensing devices on the exterior of the
drill string is that particularly with directional drilling the
exterior devices are damaged by striking the formations about the
bore hole.
[0005] In order to enhance communication with the earth's surface,
it is preferred to electrically isolate drill string components so
that electromagnetic signals can be developed for data telemetry.
This is achieved by a subassembly connector which electrically
isolates adjacent drill string components so that the isolated
components provide the two terminals of an antenna to which an
alternating current is applied in developing the electromagnetic
signal for transmission to the earth's surface. Examples of such
connectors are described in U.S. Pat. No. 6,050,353 to Ryan Energy,
U.S. Pat. No. 5,138,313 to Haliburton Company, U.S. Pat. No.
5,163,714 to Geoservice and Canadian patent application 2,151,525
to McAllister Petroleum Services, Ltd.
[0006] The various types of subassemblies provide for electrical
isolation which are particularly useful in bore hole inspection,
but may be subject to failure when used, for example, in
directional drilling. It has been found that the drill string, and
in particular the subassembly connector, is subjected to extreme
torsional compression, tension, and bending moments during
directional drilling. Such extreme forces can result in connector
failure, usually at the weakest point in the subassembly. The
connectors of these patents and patent application may fail due to
overstressing and possibly break up at their weakest point.
Furthermore, in the prior art, such as U.S. Pat. No. 4,766,442, it
is generally accepted that to prevent short circuiting of the
alternating current applied to the subassembly, a substantial gap
spacing (i.e. 50 cm or more) is necessary. These large gaps require
a protective wrapping, as the abrasive conditions during drilling
can quickly damage the insulative materials used in these gaps.
However, the protective wrapping is also subject to extreme
abrasive forces and are consequently prone to frequent failure,
thus necessitating frequent replacement.
SUMMARY OF THE INVENTION
[0007] In accordance with an aspect of this invention, provided is
an electrical isolation connector subassembly for use in data
telemetry in directional drilling applications. The electrical
isolation connector subassembly of the current invention has
enhanced strength characteristics due to a more robust design, and
incorporates a considerably smaller gap region between the
electrically isolated adjacent drill string components, thereby
reducing the amount of wear to the insulative surfaces and
eliminating the need for a protective wrapping.
[0008] In accordance with an aspect of this invention, provided is
an electrical isolation connector subassembly for interconnecting
adjacent tubular drill rods of a drilling system used in drilling
bore holes in earth formations, said connector comprising an
electrically insulative sleeve being sandwiched between two
electrically isolated subassembly components, the sleeve providing
an exterior gap between the edges of the spaced apart electrically
isolated components, the exterior gap having a width of less than
50 cm.
[0009] In accordance with an aspect of this invention, provided is
an electrical isolation connector subassembly for interconnecting
adjacent tubular drill rods of a drilling system used in drilling
bore holes in earth formations, said connector comprising: [0010] a
first electrically isolated component; [0011] a second electrically
isolated component; [0012] a plurality of insulator sleeves; [0013]
the first electrically isolated component being adapted on one end
to connect to a first tubular drill rod; [0014] the second
electrically isolated component being adapted on one end to connect
to a second tubular drill rod; [0015] said plurality of insulator
sleeves electrically separating said first and second electrically
isolated components; [0016] wherein at least one of said insulator
sleeves is sandwiched between the first and second electrically
isolated components, providing an exterior gap between the edges of
the spaced apart first and second electrically isolated components,
the exterior gap having a width of less than 50 cm. electrically
isolated
[0017] In accordance with a further aspect of this invention,
provided is an electrical isolation connector subassembly for
interconnecting adjacent tubular drill rods of a drilling system
used in drilling bore holes in earth formations, said connector
comprising: [0018] a mandrel, wherein said mandrel is adapted at
one end to connect to a first tubular drill rod; [0019] a housing,
wherein said housing is adapted at one end to connect to a second
tubular drill rod; [0020] a conductive ring located on an external
surface of said connector; [0021] a plurality of insulator sleeves;
[0022] said mandrel and said housing being electrically continuous;
[0023] said conductive ring being electrically isolated from said
mandrel and said housing by said insulator sleeves; [0024] an
electrode assembly that engages said conductive ring wherein said
electrode assembly is electrically isolated from said mandrel and
said housing, said electrode assembly being positioned within
openings in said mandrel wherein said openings extends
perpendicular to the longitudinal axis of the electrical isolation
connector subassembly; [0025] wherein said insulator sleeves are
sandwiched between the conductive ring and adjacent opposing faces
of the subassembly, providing an exterior gap having a width of
less than 50 cm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a perspective view of an assembled electrical
isolation connector subassembly of the current invention;
[0027] FIG. 2 is a section through the electrical isolation
connector subassembly of FIG. 1;
[0028] FIG. 3 is an exploded view in perspective of the electrical
isolation connector subassembly of FIG. 1;
[0029] FIG. 4 is an enlarged sectional view of the electrical
isolation connector subassembly of FIG. 1 showing further details
of the subassembly;
[0030] FIG. 5 is a perspective view of an alternate embodiment of
the electrical isolation connector subassembly, shown
assembled;
[0031] FIG. 6 is a section through the electrical isolation
connector subassembly of FIG. 5;
[0032] FIG. 7 is an exploded view in perspective of the electrical
isolation connector subassembly of FIG. 5; and
[0033] FIG. 8 is an enlarged sectional view of the electrical
isolation connector subassembly of FIG. 5 showing further details
of the subassembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Various aspects of the invention are described in detail
where it is appreciated that the principles of the invention, as
established in the detailed description of the drawings, may find
application for use in data telemetry during directional drilling
operations. The purpose of the invention is to electrically isolate
drill rod components so as to form an antenna, preferably adjacent
the location of the drill bit. The antenna transmits
electromagnetic data signals to the earth surface that are
interpreted and used for various informational purposes, such as
for the inspection and evaluation of bore holes. Quite
surprisingly, applicant has found that the external gap between the
electrically isolated components can actually be less than 50 cm.
This was never thought possible as per the prior art. By virtue of
this shortened external gap the invention can provide a robust
drilling subassembly. This shortened external gap greatly
facilitates manufacture and assembly of the subassembly. Although
the spacing may be less than 50 cm, the preferred spacing is from
about 1/2 cm to less 50 cm, or about 1 cm to about 40 cm, or more
preferably about 2 cm to about 30 cm, or about 3 cm to about 20 cm,
or most preferably about 5 cm to about 10 cm. The most preferred
range is about 5 cm to about 10 cm, from the standpoint of
machining the various components, particularly the internal
portions thereof. From the standpoint of effectiveness of signal
generation, it is appreciated as the gap is shortened, the
efficiency level decreases. However, for the preferred range of
about 5 cm to 10 cm, the system is very effective in generating a
signal and usually does not improve very much in effectiveness for
gap spacing greater than about 20 cm. These conditions, of course,
do vary depending upon the earth formation characteristics.
[0035] The electrical isolation connector subassembly generally
comprises a first electrically isolated component and a second
electrically isolated component, the two electrically isolated
components being separated by a insulative sleeves. As will be
discussed in more detail, the subassembly comprises at least one
insulative sleeve that is sandwiched between the two electrically
isolated subassembly components, the sleeve providing an exterior
gap between the edges of the spaced apart electrically isolated
components, the exterior gap having a width of less than 50 cm.
With specific reference to FIG. 1, 2 and 3, shown is an assembled
electrical isolation connector subassembly 10, ready for
installation into a drill string. The electrical isolation
connector subassembly 10 shown in these FIGS. comprises a
longitudinal bore 12, a first coupler 14, a mandrel 16, a gap
housing 18 and a second coupler 20, the components being of
circular cross-section, of the same outside diameter and coaxial
about the longitudinal axis 21. The first coupler 14 has a first
end 22 adapted to connect to a first drill string component, and a
second end 24 adapted with inwardly tapered outside-surface threads
to threadably and conductively engage the mandrel 16, the mandrel
16 having a corresponding inside-surface threaded mating surface.
The first coupler 14 and the mandrel 16 when assembled form the
first electrically isolated component, this joined assembly having
a continuous outer surface 26. The gap housing 18 and the second
coupler 20 form the second electrically isolated component. The
elongate body of the mandrel 16 has an outer surface that tapers
inwardly in a stepwise manner towards an inside end 17, in a
direction towards the second coupler 20, the steps being first step
28, second step 30 and third step 32. To prevent longitudinal axial
rotation of the gap housing 18 with reference to the mandrel 16,
the interface of these two components, that being the second step
30 and an inside surface of a first end 33 of the gap housing 18
are configured with non-circular mating surfaces so that when
assembled, the mandrel 16 and gap housing 18 are maintained in a
non-rotatable relationship to one another. The hexagonal mating
configuration is shown in FIG. 3.
[0036] To prevent electrical contact between the mandrel 16 and the
gap housing 18, there is positioned between the mandrel 16 and the
gap housing 18 a plurality of electrically non-conductive insulator
sleeves, the insulator sleeves being placed over-top the above
mentioned steps (28, 30, 32). The electrically non-conductive
insulator sleeves are removable elements that can be reused,
thereby simplifying assembly and disassembly of the connector. It
is appreciated, however, that alternative insulators could be
substituted. For example, the insulative sleeves could be formed in
place by means of a suitable insulative material injection process
for filling the space occupied by the sleeve. For the purpose of
describing the invention. the following assumes use of the
removable/reusable insulative sleeves. Positioned over first step
28, second step 30 and third step 32 is first insulator sleeve 34,
second insulator sleeve 36 and third insulator sleeve 38,
respectively. As mentioned above, the outer surface of second step
30 is non-circular to prevent longitudinal axial rotation of the
gap housing 18 with reference to the mandrel 16. Drilling torque is
thereby transmitted from the upper drill along through the
subassembly 10 to the lower drill string. Therefore, the shape of
the second insulator sleeve 36 is configured to match that of the
gap housing 18 and mandrel 16. In FIG. 3, where a hexagonal mating
configuration is represented, the second insulator sleeve 36 is
shown with the corresponding hexagonal shape.
[0037] To prevent ingress of drilling mud into the assembly, a
compression gasket 40 is positioned between mandrel shoulder 42 and
the edge of the first insulator sleeve 34 (see FIG. 4). To maintain
the insulator sleeves (34, 36, 38) in place on the mandrel 16, a
retaining nut 44 is used that threadably engages the threads 46 of
the mandrel 16, the threads 46 being located on the outside surface
of the mandrels inside end 17. By tightening the retaining nut 44,
the electrically non-conductive insulator sleeves (34, 36, 38) and
the compression gasket 40 are biased towards the respective first
shoulder 42, second shoulder 90 and third shoulder 92 machined at
each step (28, 30, 32) of the mandrel 16 so as to ensure a
contiguous electrically non-conductive layer as well as to provide
a seal against the ingress of drilling mud (see FIG. 4 for an
enlarged, more detailed view of the region containing the various
insulative sleeves, the retaining nut and other associated
components).
[0038] Positioned between the third insulator sleeve 38 and the
retaining nut 44 is an insulator spacer 48, wherein the insulator
spacer 48 prevents electrical contact between the retaining nut 44
and the gap housing 18. To lock the retaining nut 44 in place,
immediately adjacent the threads 46 of the mandrel 16 and the
retaining nut 44, to the side towards the second coupler 20, is
positioned a retaining washer 50 and a retaining clip 52. The
retaining clip 52 is received by a circumferential box-shaped
groove 54 on the outer surface of the tapered end 55 of the mandrel
16. To prevent electrical contact between the mandrel 16 and the
second coupler 20, an aft insulator 56 is positioned over the
retaining nut 44, the aft insulator 56 having an end face 58 that
abuts the insulator spacer 48. To ensure a seal between the aft
insulator 6 and the mandrel 16, the inside end 17 of the mandrel 16
is adapted to receive a plurality of O-rings 60 fitted within
circumferential box-shaped grooves 62.
[0039] To attach the second coupler 20 to the assembly, the second
coupler 20 is adapted at a first end 64 with inside-surface threads
65 to threadably and conductively engage the gap housing 18, the
gap housing 18 having a corresponding outside-surface threaded
mating surface. Upon assembly, the second coupler and gap housing
form a smooth outer surface 66. Adjacent to the end face 68 of the
aft insulator 56, is positioned a gasket 70 that is sandwiched
between the aft insulator 56 and an inside shoulder 72 of the
second coupler 20. To ensure a seal between the aft insulator 56
and the second coupler 20, the outer surface of the aft insulator
56 is adapted to receive a plurality of o-rings 74 fitted within
circumferential box-shaped grooves 76. To facilitate placement of
the electrical isolation connector subassembly 10 within a drill
string, the second coupler 20 is adapted at a second end 78 to
engage a second drill string component (See FIG. 2). To permit
labelling of the various components of the assembly with, for
example, serial numbers, the outside surface of first coupler 14,
the mandrel 16 and the second coupler 20 is machined with a
recessed flat surface.
[0040] With the electrical isolation connector subassembly 10
assembled, there are two electrically isolated regions being
separated by the contiguous insulative structure comprising the
plurality of electrically non-conductive insulator sleeves (34, 36,
38), the insulator spacer 48 and the aft insulator 56, the first
electrically isolated region comprising the first coupler 14 and
mandrel 16, and the second electrically isolated region comprising
the gap housing 18 and second coupler 20. At the surface of the
electrical isolation connector subassembly 10, the two electrically
isolated regions are separated by n exterior gap 98 that is
preferably less than 50 cm, with the gap surface being the exposed
surface of the first insulative sleeve 34 (as shown in FIG. 4). To
each side of the gap, there are wear shoulders 100, 102, the wear
shoulders 100, 102 being received in respective circumferential
recesses 104, 106 machined into the mandrel 16 and gap housing
18.
[0041] In addition, with the electrical isolation connector
subassembly 10 assembled, there is a continuous longitudinal bore
12 that runs through the electrical isolation connector subassembly
10, allowing for placement of a transmitter electrode. The
transmitter electrode 80 is housed within a wear resistant
electrically insulative wash tube (not shown) that is aligned
concentrically with the longitudinal axis 21 (see FIG. 2). To
facilitate placement of the transmitter electrode 80 on the wash
tube within the longitudinal bore 12, a centering disk or spider 81
is used. The centering disk 81 is positioned within the
longitudinal bore 12 in the non-tapered region 82 of the mandrel
16. The centering disk 81 is configured with an outside diameter
that corresponds to the inside diameter of the non-tapered region
82 of the longitudinal bore 12 and is positioned having a face 84
abutting an interior shoulder 86 of the mandrel 16 to aid in
maintaining it in a fixed position relative to the mandrel inside
surface. The centering disk 81 has an aperture 94 coaxially aligned
with the longitudinal axis 21 through which the transmitter
electrode is positioned and further comprises a plurality of
apertures 96 to facilitate the passage of drill fluid or
medium.
[0042] To operate, an alternating signal is applied to the
electrically isolated regions for transmitting an electromagnetic
signal back to the surface, for example, in the manner described in
U.S. Pat Nos. 5,138,313 and 5,163,714.
[0043] Shown in FIGS. 5, 6 and 7 are alternate embodiments of the
present invention, an electrical isolation connector subassembly
110, shown assembled and ready for installation into a drill
string. The electrical isolation connector subassembly 110
comprises a longitudinal bore 112, a mandrel 114, a housing 116, a
conductive ring 118 and an electrode assembly 120. As will be
described in more detail, the conductive ring 118 is electrically
isolated from the electrically continuous mandrel 114 and housing
116 by a plurality of insulator sleeves. The mandrel 114 has a
first end 122 adapted to connect to a first drill string component,
and a second end 124 adapted with outside-surface threads 126 to
threadably and conductively engage the housing 116, the housing 116
having a corresponding inside-surface threaded mating surface 128.
The drilling torque is transmitted through the subassembly by the
threaded connections at 126/128. The mandrel 114, the housing 116
and the conductive ring 118 each have the same outside diameter and
are coaxially aligned with the longitudinal axis 130. When
assembled, the second end 124 of the mandrel 114 abuts an inside
shoulder 137 of the housing 116.
[0044] To electrically isolate the conductive ring from the mandrel
114 and housing 116, electrically non-conductive insulator sleeves
are used, those being a first ring conductor insulator 132 and a
second ring conductor insulator 134. As mentioned in the previous
embodiment, the insulator sleeves are removable and reusable. It is
appreciated, however, that the removable/reusable insulator sleeves
could be substituted with a formed-in-place insulator using a
suitable insulative material injection process. The
removable/reusable insulator sleeves are used in the following
discussion. The ring conductor insulators (132,134) are "L" shaped,
oriented such that the outer sides (138, 140) of the short portions
(142, 144) separates the conductive ring from the adjacent
structure (the mandrel 114 in the case of the first ring conductor
insulator 132 and the housing 116 in the case of the second ring
conductor insulator 134), and with the long portion 146 separating
the underside 148 of the conductive ring 118 from the mandrel 114.
To accommodate placement of the ring conductor insulators 132, 134,
the mandrel 114 outside diameter steps circumferentially inwards,
defining a smaller diameter region 149 of the mandrel 114, the step
forming shoulder 150. An opposing shoulder 152 is formed by an end
face 154 of the housing 116. This smaller diameter portion 149 of
the mandrel 114 permits the positioning of the ring conductor
insulators (132, 134) such that when assembled, exterior gap 156,
158 of the ring conductor insulators 132, 134 remain slightly
recessed in comparison to the remainder of the assembly, and
maintain an exterior gap that is less than 50 cm in width.
[0045] The mandrel 114, the housing 116 and the conductive ring
118, in the areas immediately adjacent the exterior gap 156, 158 of
the ring conductor insulators 132, 134, are slightly recessed 160
to accommodate placement of an abrasion resistant wrapping (not
shown), the recess being sufficiently deep to align with the
exterior gap 156, 158 of the ring conductor insulators 132, 134. In
addition to the two ring conductor insulators 132, 134, there is
positioned adjacent the two long portions 146 of the ring conductor
insulators 132, 134, between the conductive ring 118 and the
mandrel 114, a central insulator 161. This central insulator 161 is
machined with apertures, to allow passage of a conductor cap 162 of
the electrode assembly 120. To prevent the ingress of drilling mud,
a plurality of seals are incorporated into the assembly (See FIG. 8
for identification of seal structures). At the surface, a
compression gasket 151 is sandwiched between the first ring
conductor insulator 132 and the shoulder 150 of the mandrel 114.
Internally, the underside of the conductive ring 118, the outer
surface of the smaller diameter portion of the mandrel 114 and the
outer surface of the second end 124 of the mandrel 114 are fitted
with O-rings 164, received by circumferential box-shaped grooves
166.
[0046] The electrode assembly 120, as shown in FIGS. 7 and 8, is
the means by which a signal is delivered to the conductive ring 118
and is positioned within an electrode aperture 167 machined in the
mandrel 114, wherein said aperture extends perpendicular to the
longitudinal axis. The electrode assembly 120 is comprised of a
conductor base 168, a spring 170, and a conductor cap 162, with the
spring 170 being positioned against the conductor base 168 and
biased to impart pressure against the conductor cap 162 thereby
causing contact between the conductor cap 162 and the conductive
ring 118. The electrode assembly 120 is electrically isolated from
the mandrel 114 by an electrically non-conductive transverse
insulator 174 that lines the electrode aperture 167 in the mandrel
114.
[0047] Positioned within the longitudinal bore 112 of the
electrical isolation connector subassembly 110, is a first wash
pipe 176 and a second wash pipe 178, each wash pipe 176, 178 being
manufactured of electrically non-conductive material and situated
having partial overlap with the transverse insulator 174 such that
the central wash pipe coupler 180 is electrically insulated from
the mandrel 114. The central wash pipe coupler 180 maintains the
transmitter electrode 182 in a coaxial alignment with the
longitudinal axis 130 of the assembly by means of a central
aperture 184. Additional apertures 186 are machined into the
central wash pipe coupler 180 to permit passage of drill mud and
material. At the end 187 opposite the central wash pipe coupler
180, the first wash pipe 176 is maintained in position by an upper
wash pipe cup 188. The upper wash pipe cup 188 is fixed within the
longitudinal bore 112 of the assembly by having chamfered shoulder
190 positioned up against a corresponding chamfered shoulder 192
machined into the inside surface of the mandrel 114. Similarly, the
second wash pipe 178 is held in position, up against the central
wash pipe coupler 180 by means of a lower wash pipe cup 194. The
lower wash pipe cup 194 is maintained in position by a snap ring
196, the snap ring 196 being received by a circumferential
box-shaped groove 198 on the inside surface 200 of the mandrel
114.
[0048] To ensure that drilling mud flows through the wash pipes
176, 178 and not around it, a plurality of seals are incorporated
into the assembly. Each wash pipe cup 188, 194 has two sets of
o-rings, sitting within circumferential box-shaped grooves, the
first set of O-rings 202 ensuring a seal between the wash pipe cups
188, 194 and the wash pipes 176, 178, and a second set of O-rings
204 ensuring a seal between the wash pipe cups 188, 194 and the
mandrel 114. Additional O-rings 206 are located on the central wash
pipe coupler 180, held within circumferential box-shaped grooves
208, positioned between the central wash pipe coupler 180 and the
wash pipes 176, 178.
[0049] As was mentioned above for the first embodiment, to send a
signal from the subassembly, an alternating signal is applied to
the electrically isolated regions for transmitting an
electromagnetic signal back to the surface, for example, in the
manner described in U.S. Pat Nos. 5,138,313 and 5,163,714.
[0050] Although preferred embodiments of the invention have been
described herein in detail, it will be understood by those skilled
in the art that variations may be made thereto without departing
from the spirit of the invention or the scope of the appended
claims.
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